In this gray and quiet city, there lives a group of children with gray wings. An organization called "Gray Feather Alliance" secretly protects them from the outside world. In this way, the silent children live a peaceful life every day. Who are they? Where do they come from? What does the wings behind them mean? The children know nothing. They were born and grew up here. They have no relatives, no hometown, and even no memories. The only thing they know is that as long as they live in this Licheng forever, they will be safe. On this day, the children welcomed their new member Luoxia (voiced by Hirohashi Ryo). As a senior, Kong (voiced by Yajima Akiko), Guang (voiced by Orikasa Fumiko) and Li (voiced by Noda Junko) accepted her arrival with joy. And this is just the beginning of the story. Slowly, when these kind and simple children know the truth of everything, can they still spread their gray wings to leave Licheng and fly into the sky?